U.S. patent number 4,947,159 [Application Number 07/182,436] was granted by the patent office on 1990-08-07 for power supply apparatus capable of multi-mode operation for an electrophoretic display panel.
This patent grant is currently assigned to 501 CopyTele, Inc.. Invention is credited to Frank J. Di Santo, Denis A. Krusos.
United States Patent |
4,947,159 |
Di Santo , et al. |
August 7, 1990 |
Power supply apparatus capable of multi-mode operation for an
electrophoretic display panel
Abstract
There is disclosed a multi-mode power supply for biasing an
electrophoretic display and particularly for biasing the anode
electrode of such a display. The supply contains first and second
supply means each of which can operate as a constant voltage or
constant current supply. The first and second supplies are
respectively coupled to the anode electrode of the electrophoretic
display so that during the Write Mode the display is operated with
a constant current at a first polarity and operates with a constant
current at a second polarity during the Erase Mode. Additional
modes are shown where AC voltages are applied to the anode
electrode either directly as in the case of a Slow Erase Mode or
via a capacitor in the case of a Time 60 Cycle Mode for a given
time period. In these modes the supplies are operated as constant
voltage sources to enable suitable magnitude voltages to be applied
to the anode electrode in order to provide optimum operating
conditions for the electrophoretic display.
Inventors: |
Di Santo; Frank J. (North
Hills, NY), Krusos; Denis A. (Lloyd Harbor, NY) |
Assignee: |
501 CopyTele, Inc. (Huntington
Station, NY)
|
Family
ID: |
22668483 |
Appl.
No.: |
07/182,436 |
Filed: |
April 18, 1988 |
Current U.S.
Class: |
345/107;
359/296 |
Current CPC
Class: |
G09G
3/3446 (20130101); G09G 2310/061 (20130101); G09G
2330/02 (20130101); G09G 2300/06 (20130101); G09G
2310/068 (20130101) |
Current International
Class: |
G02F
1/167 (20060101); G02F 1/01 (20060101); G09G
3/34 (20060101); G09G 003/00 () |
Field of
Search: |
;340/787,788,805
;350/362 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
4203106 |
May 1980 |
Dalisa et al. |
4420749 |
December 1983 |
Koyanagi et al. |
4485379 |
November 1984 |
Kinoshita et al. |
4655897 |
April 1987 |
Di Santo et al. |
4746917 |
May 1988 |
Di Santo et al. |
|
Primary Examiner: Oberley; Alvin
Attorney, Agent or Firm: Plevy; Arthur L.
Claims
We claim:
1. In an electrophoretic display of the type having an anode
electrode associated with an X-Y matrix manifesting grid and
cathode electrodes to provide a display by causing pigment
particles to be transported to said anode electrode during a Write
Mode according to drive signals applied between said grid and
cathode electrodes, the improvement therewith comprising:
constant current source means coupled to said anode electrode to
provide a constant current to said anode electrode during said
Write Mode and of a given polarity necessary to transport said
particles to said anode electrode.
2. The electrophoretic display according to claim 1, wherein said
constant current source means being coupled to said anode electrode
and operative to provide a constant current to said anode electrode
of an opposite polarity sufficient to direct said particles away
from said anode electrode, indicative of an Erase Mode.
3. The electrophoretic display according to claim 2, further
including controllable switching means coupled to said anode
electrode and capable of operating in a first mode wherein said
constant current of said given polarity is applied to said anode
electrode indicative of said Write Mode and operative in a second
mode where said constant current of said opposite polarity is
applied to said anode electrode indicative of said Erase Mode.
4. The electrophoretic display apparatus according to claim 3,
wherein said constant current source means a first constant current
source for providing constant current at given polarity at an
output with said output coupled to said switching means, and
a second constant current source for providing constant current at
said opposite polarity and coupled to said switching means and,
means for operating said switching means in said first and second
modes wherein said first mode said current source of said given
polarity is coupled to said anode electrode and wherein said second
mode and current source of said opposite polarity is coupled to
said anode electrode.
5. A power supply apparatus for biasing the anode electrode of an
electrophoretic display panel, said electrophoretic display having
an X-Y grid manifesting cathode and grid electrodes which when
driven and biased enable pigment particles to be transported and
packed on the anode electrode according to drive signals applied
between said grid and cathode electrodes during a Write Mode when
said anode electrode is biased at a first polarity and to remove
said particles as packed on said anode electrode during an Erase
Mode where said anode is biased at a second polarity, said power
supply comprising:
switching means having an output terminal coupled to said anode
electrode and operative in a first mode where said output terminal
is connected to a first input terminal and in a second mode where
said output terminal is coupled to a second input terminal,
a first power supply means having an output coupled to said first
input terminal of said switching means for providing a first
polarity biasing signal for said anode electrode when said
switching means is operated in said first mode,
a second supply means having an output coupled to said second input
terminal and operative to provide a second polarity biasing signal
when said switching means is operated in said second mode,
with each of said first and second supply means including separate
means for monitoring the current through said anode electrode with
respect to a reference level to maintain a constant output current
according to said monitored current when said first or second
supply means is connected to said anode electrode by said switching
means, whereby when said first supply means is connected to said
first input terminal said associated means for monitoring is
operative to maintain a constant current from said first supply
means and when said second supply means is connected to said second
input terminal said associated means for monitoring is operative to
maintain a constant current from said second supply means.
6. A power supply apparatus for applying operating potential to the
anode electrode of an electrophoretic display panel,
comprising:
a first supply means capable of being selectively operated as a
constant current supply in a first mode and a constant voltage
supply in a second mode, switching means coupling said anode
electrode to said first supply means during a Write Mode and means
for selecting said first supply means to operate as a constant
current supply during said Write Mode.
7. The power supply apparatus according to claim 6, further
including:
a second supply means capable of being selectively operated as a
constant current supply in a first mode and a constant voltage
supply in a second mode,
said switching means coupling said anode electrode to said second
supply means during an Erase Mode and means for selecting said
second supply means to operate as a constant current supply during
said Erase Mode.
8. The power supply apparatus according to claim 7, further
including means coupled to said switching means for operating said
switching means at a given rate,
means coupled to said first and second supply means for operating
said supplies as constant voltage supplies whereby the voltage
outputs of said first and second supply means are respectively
applied to said anode electrode at said given rate to provide a
Slow Erase Mode for said panel.
9. The power supply apparatus according to claim 8, wherein said
given rate is between 1 to 3 HZ.
10. The power supply apparatus according to claim 9 further
including means coupled to said switching means for selectively AC
coupling said switching means to said anode electrode,
means coupled to said switching means for operating said switching
means at another given rate,
with said selector means operative to cause said first and second
supply means to operate as constant voltage supply means whereby
said first and second supply means are respectively applied to said
anode electrode via a to provide an AC coupled signal to said anode
electrode when said anode electrode is AC coupled to said first and
second supply means.
11. The power supply apparatus according to claim 10 wherein said
another given switching rate is approximately 60 HZ.
12. In an electrophoretic display panel of the class having an
anode display electrode, at least one cathode electrode located
apart from said anode electrode and directed in a given plane and
at least one grid electrode insulated from said cathode electrode
and positioned transverse thereto with the space between said
anode, grid and cathode electrodes filled with charged pigment
particles suspended in a dye solvent wherein said particles can be
transported to said anode electrode according to driving potentials
applied between said grid and cathode electrodes indicative of a
desired pattern during a Write Mode where said anode electrode is
biased at a first polarity operating level and where said particles
are removed from said anode electrode during an Erase Mode where
said anode electrode is biased at a second polarity operating
level, the combination therewith of power supply apparatus for
biasing said anode electrode during said Write and Erase Modes
comprising:
constant current source means coupled to said anode electrode for
providing said first polarity operating level at a constant current
during said Write Mode whereby said anode current is maintained
relatively constant during said Write Mode and,
said constant current source means being responsive to said display
being operated in said Erase Mode to provide said second polarity
operating level to said anode electrode at a constant current
during said Erase Mode.
13. The apparatus according to claim 12, wherein said means
responsive to said display being operated in said Erase Mode
includes switching means coupled to said anode and wherein said
constant current source means includes a first current source
applied to said anode during a first mode of said switching means
indicative of said Write Mode and a second current source applied
to said anode during a second mode of said switching means
indicative of said Erase Mode.
14. The apparatus according to claim 12, further including means
for selectively AC coupling said anode electrode to first and
second voltage sources via common switching means and for operating
said switching means at a given rate to selectively apply said
first and second voltages to said anode electrode at said given
rate.
15. The apparatus according to claim 14, including means coupled to
said switching means for selectively operating said switching means
at a lower given rate and including means coupled to said first and
second current sources to operate said first and second current
sources as first and second voltage sources to enable voltage
outputs of said first and second voltage sources to be applied
directly to said anode electrode at said lower given rate.
16. The apparatus according to claim 15, wherein said lower given
rate is between 1-3 HZ per second.
17. The apparatus according to claim 14, wherein said given rate is
approximately 60 HZ.
Description
BACKGROUND OF INVENTION
This invention relates to electrophoretic displays in general and
more particularly to a power supply for properly biasing and
maintaining reliable operation of such a display.
The prior art is replete with many references which relate to
electrophoretic displays. Reference is made to U.S. Pat. No.
4,655,897 issued on Apr. 7, 1987 to Frank J. DiSanto and Denis A.
Krusos, the inventors herein, and assigned to Copytele, Inc., the
assignee herein. Essentially, that patent discloses an
electrophoretic display apparatus which includes a planar
transparent member having disposed on the surface a plurality of
vertical conductive lines to form a grid of lines in the Y
direction. On top of the grid of vertical lines there is disposed a
plurality of horizontal lines in the X direction which are
positioned above the vertical lines and insulated therefrom by a
thin insulating layer at each of the intersection points.
Spaced above the horizontal and vertical lines patterns is a
conductive anode plate. The space between the conductive plate and
the X and Y line patterns is filled with an electrophoretic
suspension containing chargeable pigment particles. When a voltage
is impressed between the X and Y lines, pigment particles which are
located in wells or depressions between the X and Y pattern are
caused to migrate toward the conductive plate and are deposited in
accordance with the bias and drive signals supplied to the X and Y
line conductors.
The patent also describes the operation and fabrication of such
displays. In any event, there are many other references which
pertain to electrophoretic displays.
Basically, as indicated above, the electrophoretic display consists
of a suspension of pigment particles dispersed in a dye solvent of
contrasting color. The solvent as well as the particles is placed
into a cell which basically consists of two parallel and
transparent conducting electrodes designated as the anode and
cathode. Many such cells in the prior art also employ a grid
electrode which further controls the transportation of charged
particles. See the above-cited patent for an examples of this type
of display.
In operation the charged particles are transported and forced
against one electrode as the anode or cathode under the influence
of an applied electric field so that the viewer may see a desired
pattern formed by pigment particles. When the polarity of the field
is reversed, the pigment particles are transported and packed on
the opposite electrode. As indicated, the prior art is cognizant of
such devices.
A particularly interesting application which is copending herewith
is entitled METHOD AND APPARATUS FOR OPERATING AN ELECTROPHORETIC
DISPLAY BETWEEN A DISPLAY AND A NON-DISPLAY MODE, filed on July 14,
1986, Ser. No. 885,538, U.S. Pat. No. 4,746,917, for Frank J.
DiSanto and Denis A. Krusos, the inventors herein, and assigned to
the assignee, Copytele, Inc.
In that application there is shown an electrophoretic display which
is operated in a first mode where the display operates to display
data and has normal DC voltages applied to its electrodes. During a
second mode or a non-display, mode a suitable alternating voltage
of a given frequency and magnitude is AC coupled to the anode
electrode of the display for a predetermined time interval to cause
pigment particles to settle between the anode and cathode whereby
the effective life of said display is increased. The transfer of
the display mode to the second mode is afforded by suitable
switching circuitry.
That application describes the biasing of the various electrodes of
the electrophoretic display and particularly describes operation
during a non-display mode and a display mode.
As seen in that application, there is shown the various electrodes
associated with the electrophoretic display and the biasing of the
electrodes in the first and second modes. The patent application
shows various relays which are utilized to power the display during
the operational mode and to remove power from the display during a
non-operating mode.
The electrophoretic display has a particular advantage in that once
data is written into the display, the data can remain displayed for
extended periods of time without the utilization of any biasing
potential.
The electrophoretic display operates in many modes. One mode is the
Write Mode. In the Write Mode the anode voltage is positive to
allow pigment particles to migrate to the anode under control of
signals applied to the grid and cathode. During an Erase Mode,
particles which migrated to the anode are removed from the anode
thus erasing the display. In the Erase Mode the anode is negative.
There is also a Hold Mode. During the Hold Mode, the anode voltage
is positive and essentially the Hold Mode is similar to the Write
Mode in that the anode is positive and is awaiting the receipt of
data. As one will understand, the electrophoretic display is
changed during operation from the Hold or Write Mode to the Erase
Mode to thereby erase data and then write data back into the
display.
This is a typical operation. In order to perform such operations,
the anode voltage, as will be explained, is switched between a
positive and a negative level indicative of the Write or Hold Mode
as compared to the Erase Mode. There are other modes which are
associated with the electrophoretic display one of which is
indicated in the above-referenced co-pending application. In these
modes the anode electrode is supplied with suitable AC operating
potentials either coupled to the anode electrode via a capacitor or
directly applied to the anode electrode at relatively slow rates.
The technique of applying an AC signal to the anode is described in
regard to the above-noted co-pending application to prevent
agglomeration clustering.
The electrophoretic display has been analogized in operation to
that of a vacuum tube triode. Hence, the various electrodes for
such a display have been designated as the anode, the grid and the
cathode. While the analogy has some basis in regard to
understanding operation of the display, an electrophoretic display
is subjected to many variations which are not provided in a typical
vacuum tube triode. As noted, the electrophoretic display is
associated with a suspension of pigment particles dispersed in a
dye solvent of contrasting color. This affords the medium through
which the particles are directed to the anode or cathode of the
display. Due to this medium, the characteristics of the display
vary greatly. These variations depend upon the recent history of
the display such as when it was last operated and in what mode.
Certain of the characteristics of the display depend on the
operating temperature as well as how long the display was inactive.
Most of these phenomenon are due to the chemical nature of the
suspension as well as the characteristics of the solvent and
pigment particles.
In particular it is indicated that when the anode electrode of such
a display is switched to the Erase Mode or the Hold Mode, the anode
current peaks to a value as high as four times the steady state
current then falls to a value somewhat below the steady state
current and finally settles to the steady state current. In the
case of switching the anode to the Hold Mode the high peak current
decreases the amount of pigment left in the wells of the display
and thereby decreases the brightness of the display. In addition,
since the initial data applied to the panel drives all the grids
positive and the anode current is higher than steady state at this
time, a larger amount of pigment is moved from the wells than would
normally be the case if the anode current were at steady state.
The brightness of the panel is therefore reduced. Furthermore, as
indicated above, the anode current as a function of anode voltage
is dependent upon the recent history of the panel such as when it
was last operated and in what mode. In addition, the dip in anode
current, below steady state, may cause the initial portion of the
image to be lighter than the remaining image which is written when
the anode current has reached steady state. Thus, as one can
ascertain from the above, the effective impedance of the
electrophoretic display varies as a function of these different
conditions. This impedance variation of the display effects the
display brightness.
It has been found that by utilizing a constant current supply to
drive the anode of such a display, many of the above-noted problems
are avoided.
It is an object of the present invention to provide optimum
operation of electrophoretic displays by biasing the anode of the
display with a constant current source.
It is a further object of the present invention to provide an
electrophoretic display which is capable of displaying a uniform
bright image by biasing said display with a constant current source
during the Hold, Write and Erase Modes.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT
In an electrophoretic display of the type having an anode electrode
associated with an X-Y matrix manifesting grid and cathode
electrodes to provide a display by causing pigment particles to be
transported to said anode electrode during a Write Mode according
to drive signals applied between said grid and cathode electrodes,
the improvement therewith comprising constant current source means
coupled to said anode electrode to provide a constant current to
said anode electrode during said Write Mode of a polarity necessary
to transport said particles to said anode electrode.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a detailed block diagram showing a multi-mode power
supply operating in conjunction with an electrophoretic display
panel.
FIG. 2 is a schematic diagram showing a first control circuit
schematic for use with the invention to enable the power supply to
be operated in a constant current or constant voltage mode.
FIG. 3 is a schematic diagram showing a second control circuit
schematic used in this invention.
DETAILED DESCRIPTION OF THE FIGURES
Referring to FIG. 1, there is shown in diagrammatic view an
electrophoretic display panel 10. Electrophoretic panels such as
panel 10 as indicated above are fairly well known. Such panels
include a suspension of colored charged pigment particles which are
usually suspended in a dye solvent of contrasting color generally
indicated by reference numeral 20. The charged particles are
transported and packed against one electrode under the influence of
an electric field to produce a desired pattern. This occurs during
a Write Mode. Operation of electrophoretic panels as 10 can be
compared to the operation of a vacuum tube triode. Hence, such
panels include an anode electrode 11, a cathode electrode 13 and a
grid electrode 12. The grid electrode allows for the selective
transfer of pigment particles between the anode and cathode. The
display is biased by a suitable electric field applied between the
anode electrode 11 and the cathode electrode 13.
As is indicated, the electrodes as the anode, cathode and the grid
are normally maintained at suitable DC biases during the Write Mode
of the electrophoretic panel 10. These biases are supplied
respectively by suitable biasing supplies such as supply 15 for the
cathode electrode and supply 16 for the grid electrodes. Both
supplies 15 and 16 are referenced to actual ground. The cathode and
grid electrodes are further associated with driver circuits such as
amplifiers and gates which are biased from the supplies 15 and 16
and which have suitable drive signals applied to their inputs for
display writing according to those signals. The anode, as
indicated, is coupled to the power supply of the present invention
and which supply floats with respect to actual circuit ground.
In the Hold Mode the cathode electrode 13 is positive with respect
to the grid electrode. The operation of such displays is specified
in the above-noted co-pending application.
As will be explained, the anode electrode 11 is capable of being
operated in many modes to satisfy the various conditions associated
with electrophoretic displays. It is the main object of the present
invention to drive the anode electrode with a constant current
during the Hold, Write and the Erase Modes to thereby assure that
the amount of current which flows through the anode is relatively
constant. In this manner, the prior art problems of electrophoretic
displays as indicated above are circumvented.
Before proceeding with an explanation of the operation of FIG. 1,
the following descriptions are deemed to be necessary in fully
understanding the invention.
As indicated, an electrophoretic display 10 is capable of operating
in many modes which modes are implemented by means of suitable
logic circuitry which logic circuitry exists in order to write into
the display, erase the display and to further control operation of
the display. In the so-called Write Mode, the anode electrode 11
has applied thereto a positive voltage to enable particles to
migrate to the anode as controlled by the bias applied between the
grid and cathode electrodes.
A second mode is indicated as a Hold Mode. In this mode the anode
is also positive. The Hold Mode basically is defined as that mode
whereby the display is waiting to receive data, and hence the Hold
Mode is implemented prior to a Write Mode and may also be
considered to be part of the Write Mode as a Hold/Write Mode.
A third mode is the Erase Mode whereby the anode 11 has a negative
potential applied thereto to enable particles which have been
received by the anode to be removed from the anode. In the Erase
Mode the anode 11 is negative with respect to the other
electrodes.
As will be further explained, there are additional modes to which
the anode is subjected to. One mode is a Timed 60 Cycle Mode. This
is designated in FIG. 1 as T60. In this mode a 60 HZ signal is
applied to the anode electrode via a capacitor. The application of
60 cycles via the capacitor serves to rejuvenate the display during
periods of non-use. Hence, one can apply a 60 cycle signal of a
suitable amplitude during the T60 Mode to prevent certain of the
problems as described above in the co-pending application.
An AC 5-Second Mode (AC 5-S) occurs before the Write Mode. In this
mode a 60 cycle AC signal is applied to the anode electrode 11 via
a capacitor for a suitable period before the Hold Mode or Write
Mode is entered into. The AC signal applied for a suitable
interval, such as 5 seconds, which causes the charged particles to
be properly suspended in the solvent between the cathode and anode.
This signal operates to prevent the same problems as the T60
signal, namely, to prevent agglomeration and clustering.
There is also an Erase Slow Mode which will be explained. In the
Erase Slow Mode the anode electrode 11 is switched between a
negative and positive voltage which is applied to the anode
electrode 11 directly and not through a capacitor as employed
during the T60 and AC 5S Modes. This mode has not been previously
described.
Again referring to FIG. 1, there is shown the anode electrode 11
coupled to a common terminal 20 of a relay contact 21. The relay
contact 21 is associated with an output terminal 22 and another
terminal 23. Relay contact 21 is controlled by a relay coil 24
which is indicated as the B-coil. As seen in FIG. 1, contacts 20
and 22 are shunted by a capacitor 25. When the relay B-coil 54 is
operated, contact 21 moves from terminal 22 to terminal 23 thus
placing the capacitor 25 in series with the anode electrode 11.
Terminal 22 as seen is coupled to a common terminal 30 of contact
31.
Contact 31 is associated with a relay A-coil 32. Contact 31 as
shown in the Figure is in contact with terminal 33, and when the
relay A is operated, contact 31 contacts terminal 34. In this
manner, the relay coil 32 controls operation between the Hold/Write
Mode and the Erase Mode. There is shown two high voltage constant
current and constant voltage control circuits 40 and 41. Each
control circuit 40 and 41 is identical in circuit configuration. As
will be explained, each control circuit is capable of providing in
conjunction with a high voltage power supply as 42 and 43 either a
constant output voltage or a constant output current which is
directed to the electrophoretic display's anode 11 according to the
mode of operation.
Each of the high voltage supplies designated as +HV and -HV are
conventional supplies available from many manufacturers. Such high
voltage supplies for example operate as follows. They have a
control input as inputs 45 and 46 which control input receives an
operating potential and depending upon the magnitude of the
operating potential will provide a high voltage output of a
suitable magnitude. Typical supplies for example will provide about
45 volts output for a one volt input. Such supplies as 42 and 43
are available from many manufacturers including a company called
Gamma High Voltage Research Inc. of 30 North MacQuesten Parkway,
Mt. Vernon, N.Y.
The high voltage supplies 42 and 43 as well as the control circuits
40 and 41 have a common return designated as -HV and +HV which is
coupled to a common return of a floating power supply 50. The power
supply 50 provides a +12 volt and -12 volt output which outputs are
utilized to bias operational amplifiers in the control circuits.
Each of the control circuits as 40 and 41 have a control (+1 and
-1) input which is associated with a relay in each control circuit.
The relay associated with each control circuit as 40 and 41 is
operated during the various modes to thereby enable the desired
bias to be applied to the anode electrode 11 of the electrophoretic
display 10.
This bias may be a positive voltage, a negative voltage or an
alternating voltage which is AC coupled via the capacitor 25 or an
alternating voltage which is direct coupled. Both control circuits
as 40 and 41 control the respective high voltage modules 42 and 43.
Module 42 provides a given magnitude positive high voltage as
controlled. Module 43 provides a given magnitude negative high
voltage as controlled by circuit 41. Each control circuit as 40 and
41 operates to control the respective power supply as 42 and 43 in
a constant current or constant Voltage Mode depending on the
operation of the relay associated with each circuit.
As can be seen in FIG. 1, the +HV control 40 is associated with a
input OR gate 60. The input OR gate 60 serves to operate a driver
and an associated relay associated with the circuit 40. The OR gate
60 which essentially is a standard gate has the inputs, Erase Slow,
Erase, T60 and AC 5S. During any of the above conditions, the relay
associated with the control supply 40 is operated. In a similar
manner, the control supply 41 has an OR gate 61 associated
therewith which OR gate has the inputs indicated as Hold, Write,
T60, AC 5S and Erase Slow associated therewith.
The relay associated with the control supply 41 is operated when
any of the inputs to OR gate 61 go high. As seen, there are two
additional power supplies designated as 62 and 63. Supply 62 is a
+12 volt supply having a normal ground return while supply 63 is a
+5 volt supply having a normal ground return. The supply 63 is
utilized as a biasing source for the OR gates 60 and 61 while the
additional supplies are utilized for operation of the control
circuits 40 and 41. It is understood that the common return for the
control circuits 40 and 41 and the high voltage supplies 42 and 43
are directed to the common return of supply 50. Hence, all the
above-noted modules float with respect to actual ground.
As will be explained, the nature of the common return associated
with the control circuits 40 and 41 and the high voltage power
supplies 42 and 43 enable the anode current of the electrophoretic
display to be sensed by suitable resistors associated with the
control circuits 40 and 41. In this manner, the control circuits
control the associated power supplies 42 and 43 so that they can be
operated in a constant current mode where the associated resistors
sample the total anode current or can be operated in a constant
voltage mode during other operating modes associated with the
electrophoretic display.
As one can further determine from FIG. 1, both the relay coils 32
and 24 are associated with a plurality of gates. These gates are
AND or OR gates and essentially are shown in FIG. 1 in their
functional relationship. It is, of course, understood that many
different configurations can be employed for the gates such as the
use of suitable relay contacts or other logic circuitry to
implement the gating functions as shown in FIG. 1. During the T60
mode as well as the AC 5S Mode, both relay coils 24 and 32 are
operated. Relay coil 24 is operated via OR gate 71 whereby contact
21 moves to the dashed line position, and hence capacitor 25 is in
series with the anode electrode 11 of the electrophoretic display.
In both these modes relay coil 32 is operated so that a suitable 60
cycle signal is applied via gate 70 which 60 cycle signal is
derived from an oscillator or other source 74. In this manner
during both the AC 5S and T60 Modes, AND gate 70 and 72 serve to
operate relay coil 32 at the 60 cycle rate thereby switching
contact 31 between terminals 33 and 34. During this mode, as will
be explained, both the high voltage generators 42 and 43 as
controlled by the control circuits 40 and 41 operate in a constant
voltage mode.
Hence in the T60 and AC 5S Modes the contact 31 associated with
relay A or coil 32 operates at a 60 cycle rate to apply a 60 cycle
signal via capacitor 25 to the anode electrode of the display.
During the Erase Slow Mode as indicated by gate 73, a low frequency
signal such as one to three cycles obtained via generator 75 is
applied to the anode. It is seen that during the Erase Slow Mode,
the relay coil B or coil 24 is not operated. Hence, the low
frequency signal indicative of the switching rate applied to relay
coil 32 is applied directly to the anode electrode 11 of the
display. This causes the anode electrode to switch from a positive
high voltage to a negative high voltage at a one cycle or other low
frequency interval. This provides a slow erasing of the display or
removes particles from the display in a controlled manner to
further assure that the display operates correctly and that prior
art problems as agglomeration and clustering do not occur.
It is thus seen briefly from the above that the display is capable
of operating with different voltages applied to the anode electrode
11 during different modes of operation which are necessary to
enable proper and efficient operation of the display as will be
further explained.
Referring to FIG. 2, there is shown a circuit diagram of the -HV
constant control circuit 41. FIG. 3 shows the circuit diagram for
the +HV control circuit 40. At the onset, it is understood that
circuits 40 and 41 employ many identical components but as
explained are operative during different modes of the
electrophoretic display operation. The circuit of FIG. 2 differs
from the circuit of FIG. 3 in that there is included in FIG. 2 an
additional amplifier 91 which is an inverting amplifier. This
amplifier 91 is omitted in the circuit of FIG. 3. The purpose of
amplifier 91 in the control circuit 41 is to account for the
reverse current flow through resistor 85 for the -HV control
circuit operation. The circuits control the +HV supply 42 in the
case of control circuit 40 and the -HV supply 43 in the case of the
control circuit 41. It is expressly understood that both the +HV
supply 42 and the -HV supply 43 have input and output commons and
an input electrode for control and an output electrode for
developing the respective high voltages. The commons of both
supplies are wired as shown in FIG. 1 and all are returned to a
common floating ground.
Referring again to FIG. 2 and FIG. 3, there is shown an input
driver 80 which is associated with a relay coil 81. The relay coil
81 selectively operates contacts 83 and 84. The input driver 80
receives the output of gate 60 in the case of the +HV constant
control circuit 40 or receives the input from gate 61 in the case
of the -HV constant control circuit 41. In this manner, the relay
coil 81 when energized switches the contacts 83 and 84 from the
position shown in FIG. 2 and FIG. 3 to the dashed line positions.
As seen in FIG. 2 and FIG. 3, there is a resistor 85. The resistor
85 has one terminal connected to the common return 90 which
terminal is directed to the contact 83. The other terminal of
resistor 85 is connected to actual circuit ground. Thus as shown in
the Figure, when the relay coil 81 is not energized by the driver
80, the resistor 85 appears from the common lead 90 to ground.
Thus, the resistor 85 senses the total anode current of the supply
due to the floating ground arrangement.
This current which flows through resistor 85 produces a voltage at
the ground lead of resistor 85 relative to lead 90. This voltage is
sensed by means of the amplifier 91 for the -HV control circuit 41
which provides an output voltage according to the amount of current
flowing through resistor 85. In the case of FIG. 3, the voltage
across resistor 85 is secured by amplifier 92 which provides an
output voltage according to the current flow through resistor 85.
Hence the output voltage designated as V6 at the output of
amplifier 91 varies according to the current flowing through
resistor 85 for circuit 41. The output of amplifier 91 is directed
through contact 84 where it goes to one input V1 of the amplifier
92. The other input of amplifier 92 goes to a resistor 93 which has
one terminal coupled to a potentiometer 94 in parallel with a Zener
diode 95 and receives operating potential from the +12 volt supply
through resistor 96. The +12 volt supply is taken from supply 50
which as shown in FIG. 1 has a common lead connected to the common
terminal 90 of both the control circuit 40 and 41.
In a similar manner, the amplifiers as 91 and 92 are biased from
the supply 50 to enable them to exhibit both positive and negative
output voltages. In any event, the amplifier 92 provides an output
voltage proportional to the voltage at its two input terminals. The
voltage from the output of amplifier 91 is designated as V1. The
amplifier 91 will produce an output voltage which basically is
proportional to -V5. This output voltage is strictly dependent upon
the magnitude of the resistances associated with the amplifier. The
output of amplifier 92 is also a function of the current flowing
through resistor 85 as is the case of both FIGS. 2 and 3. The
output of amplifier 92 is directed to one input of an amplifier
100. The other input of amplifier 100 is coupled to a reference
Zener diode 101 which is biased through a resistor 120 and coupled
to the 12 volt supply terminal of supply 50. The output of
amplifier 100 is coupled to the base electrode of a first
transistor 102 having its emitter electrode coupled to the base
electrode of a second transistor 103. The emitter electrode of
transistor 103 is connected directly to the control electrode of
the respective supplies 42 and 43.
Hence for the +HV control 40 the emitter electrode of transistor
103 is coupled to control electrode 45. For the -HV control circuit
41 the emitter electrode of transistor 103 in that circuit is
coupled to the control electrode 46. It is understood that the
common terminal as 90 for both the circuit 40 and 41 is coupled to
the commons of each high voltage supplies as 42 and 43 and is also
coupled to the common of the floating supply 50.
As can be seen from the above, the operation of the circuit
essentially has been described for the relay coil 81 not being
energized and therefore the contacts 83 and 84 of the relay coil 81
are shown in the closed position. It is understood that when the
driver 80 energizes the respective coil 81, the contacts 83 and 84
move to the dashed line position. As will be further explained,
when the contacts are in the position as shown in FIG. 2 and FIG.
3, the control circuits 40 and 41 operate as to provide a constant
current output via the high voltage generators 42 and 43. This
constant current output is provided as the circuit monitors the
current flowing through resistor 85 and produces a control voltage
to the high voltage supply according to the voltage provided across
resistor 85 as due to the current flowing through the anode 11 of
the display.
As one can see, when the relay coil 81 is energized via amplifier
80, contacts 83 and 84 are placed in the dashed line position. As
seen in the dashed line position, resistor 85 is no longer in
circuit and the output of amplifier 91 is disconnected from the
input V1 of amplifier 92. When the relay coil is operated as
indicated above, the input V1 of amplifier 92 is connected to the
terminal V2 of the voltage divider including resistor 93 and
potentiometer 94. Hence, when the relay coil operates the contacts
83 and 84 to the dashed line position, the output of amplifier 92
produces a constant voltage as does the output of amplifier 100
which causes the emitter electrode of transistor 103 to also
provide a constant voltage and hence causing the high voltage
supply 42 and the high voltage supply 43 to produce a constant
voltage during the operation of the respective relays in circuits
40 and 41.
Thus it is clear that both the control circuits 40 and 41 utilize a
similar circuit configuration as shown in FIG. 2 and FIG. 3. The
following operations will now be explained in regard to the
above-noted operating modes of the electrophoretic display 11.
THE HOLD/WRITE MODE
As indicated and by referring to FIG. 1, contact 31 of relay coil
32 is in contact with terminal 33. Relay coil 24 is not operated
and hence capacitor 25 is shorted out. During this mode which is
the Hold/Write Mode, the driver 80 of circuit 40 is not operated by
means of the OR gate 60. In this case the contacts 83 and 84
associated with the control circuit 40 are in the position shown in
FIG. 2. Thus the output of transistor 103 causes the +HV supply 42
to provide a varying output voltage or to provide a constant
current due to the fact that resistor 85 associated with control
circuit 40 is monitoring the current through the anode electrode 11
of the electrophoretic display. In this Hold/Write Mode the gate 80
associated with control circuit 41 operates as indicated via the OR
gate 61. Hence during this condition, the control circuit 41 has
the contacts 83 and 84 in the dashed line position and essentially
the output from the supply 43 is a constant voltage which is
coupled to terminal 34 of relay contact 31 and which as indicated
in FIG. 1 is not in any manner applied to electrode 11. It is
immediately understood that the activation of the coil 81 during
the Hold/Write Mode is completely necessary to remove resistor 85
from the common lead 90 so that the total current is only monitored
by the resistor 85 associated with the control circuit 40 and not
also by control circuit 41.
THE ERASE MODE
As indicated again in FIG. 1, during the Erase Mode, relay coil 32
is operated where contact 31 goes from the position shown in FIG. 1
to the dashed line position. In the dashed line position contact 31
contacts terminal 34. Again, in the Erase Mode the relay coil B or
24 is not operated and hence terminal 34 is directly coupled to the
anode electrode 11 of the electrophoretic display. During the Erase
Mode, the driver 80 associated with the control circuit 40 is
operated. Hence, during the Erase Mode, the contacts 83 and 84
associated with control circuit 40 are moved to the dashed line
position thus removing the resistor 85 and removing the output of
amplifier 91 for control circuit 40.
As again seen in FIG. 1, during the Erase Mode, the relay coil 81
associated with the control circuit 41 is not operated. Hence the
control circuit 41 operates to supply a varying voltage to the high
voltage supply 43 to operate that supply in a constant current
mode. It is again noted that a constant current will be applied to
the anode electrode 11 of the electrophoretic display which
constant current is provided by the same operation as the current
supplied during the above described Hold/Write Modes.
It is noted that in this mode the output from the high voltage
supply 42 is not applied in any manner to the anode electrode of
the electrophoretic display. It is of course understood as
explained that the Hold/Write Mode as indicated above can be
implemented as a two-stage operation or be a single mode as the
biasing and operation of the electrophoretic display for the Hold
and Write Modes is identical. As one can understand, during Erase,
Write or Hold, the electrophoretic display receives a constant
current during each of the modes as afforded by the control circuit
40 or 41 as coupled to the respective high voltage supplies 42 and
43. This constant current eliminates the problems described in the
Background of the Invention and assures that the display will
exhibit uniform brightness when being operated between the Hold,
Write and Erase Modes.
ERASE SLOW MODE
As one can immediately ascertain, during the Erase Slow Mode, both
gates 60 and 61 are operated. In this manner both drivers 80 in
each control circuit as 40 and 41 operate the respective coils 81
to place the contacts in the dashed line position. Hence in the
Erase Slow Mode both supplies are constant voltage supplies as
controlled by the control circuits 40 and 41. In the Erase Slow
Mode as indicated above, gate 73 is operated allowing a 1 HZ or low
frequency signal via generator 75 to be applied to operate relay
coil A which moves contact 31 between terminals 33 and 34 at the
frequency provided by the generator 75. Relay coil B is not
operated and hence the output available at terminal 30 of contact
31 is directly coupled to the electrophoretic anode electrode 11.
This switches the anode 11 from a positive DC to a negative DC or
provides a direct coupled signal which causes the particles which
adhered to the anode electrode to migrate back into the solution.
Since the switching rate is very slow, the operation provides a
slow erase which operates to rejuvenate the display without the use
of the series capacitor 25.
THE T60 MODE
Again, in the T60 Mode both gates 60 and 61 of FIG. 1 are high
causing the contacts 83 and 84 of the control circuits 40 and 41 to
be in the dashed line position causing both supplies 42 and 43 to
operate as constant voltage supplies. As was explained, during the
T60 Mode, the output of AND gate 72 applies a 60 cycle signal from
generator 74 which signal operates the relay coil 32 at a 60 cycle
rate.
Relay coil B or coil 24 is operated via gate 71 to thereby couple
the output voltage at terminal 30 of contact 31 to the anode
electrode 11 via the capacitor 75. It is of course understood that
during the T60 Mode, the contact 31 moves at a 60 cycle rate
between terminals 33 and 34 and both supplies 42 and 43 operate at
a constant voltage which voltages are AC coupled via capacitor 25
to the electrode 11 of the display at the 60 HZ rate.
THE AC 5 MODE
During this mode, both gates 60 and 61 are operated to thereby move
the contacts 83 and 84 to the dashed line position to cause both
the control circuits 40 and 41 to provide a constant voltage output
via supplies 42 and 43. During this mode, relay A is operated again
at a 60 cycle rate via gate 70. Relay B is also operated so that
contact 21 is in position 23 allowing the 60 cycle AC signal be
applied to the anode electrode 11 of the electrophoretic display
via the capacitor 25. In this manner the signal is applied for a
time period of 5 seconds or thereabouts. The operation is the same
as the T60 mode with the exception that the time period is
implemented for a suitable fixed period such as 5 seconds.
It is one objective to apply this signal for a duration before
writing again into the display, and as indicated above, the
application of such a signal for suitable time durations and a
suitable frequency and amplitude is described in the above-noted
copending application.
As one can see from the above, it is necessary to provide a
multi-mode operating power supply apparatus in order to properly
bias and operate an electrophoretic display panel. In this manner
the display can be efficiently operated during the various modes as
described above. It is also understood that the various modes as
indicated above for example Hold, Write, Erase and so on are
provided by means of additional logic circuitry which is cognizant
of when the display is to receive data or be placed in the Write
Mode or to have data erased as to be placed in the Erase Mode or to
be placed in any of the additional above-described modes.
This operation can be afforded by means of a microprocessor or any
other suitable control logic in order to operate the
electrophoretic display in the above-described modes and to be
assured that the control circuits 40 and 41 serve to operate the
power supplies 42 and 43 in the appropriate modes as either
exhibiting a constant voltage or a constant current. Both the power
supplies 42 and 43 are conventional supplies and operate to produce
an output voltage according to the magnitude of a control signal
applied to input control electrodes 45 and 46. The typical output
of each supply is about 200 to 250 volts for electrophoretic
display operation. In this manner the supply 42 supplies
approximately a positive 200 volt DC while supply 43 supplies
approximately a negative 200 volt DC output.
As one can ascertain, the utilization of the control circuits 40
and 41 in combination with the high voltage supplies 42 and 43 as
associated with the electrophoretic display enables proper and
constant operation of the display. Due to the constant current
modes in the Hold, Write and Erase Modes, the display provides a
uniform brightness as compared to a prior art display.
There is a further need for these supplies to be operated in a
constant voltage mode whereby the current sensing resistors are
removed from the circuit by means of the associated relays. It is
also understood that in FIG. 2 and FIG. 3 various components which
have not been designated by specific reference numerals have
associated therewith the actual value of the component. As for
example, resistor 96 has the designation 100 which means that
resistor 96 is a 100 Ohm resistor. Resistor 94 is a potentiometer
which is 10,000 Ohms. The amplifiers 91, 92 and 100 are MC4741's
which is an integrated circuit amplifier available from many
manufacturers. In a similar manner resistor 85 is also associated
with the numeral 39 K which means that it is a magnitude of 39,000
Ohms. The various voltages associated with the operational
amplifiers such as +12 and -12 are obtained from supply 50. The
biasing for the driver 80 is obtained from supply 63 of FIG. 1
which is referenced to actual ground. The +12 volts supply
associated with relay coil 81 is obtained from supply 62 of FIG.
1.
The +12 volt supplies for transistors 102 and 103 is obtained from
supply 50 which is the floating supply as is the +12 volt supply
for the Zener diodes 95 and 101.
Thus in view of the above, it is indicated that the utilization of
the above multi-mode operating supply avoids many of the problems
as indicated in the Background of the Invention and enables an
electrophoretic display to operate with a constant current in both
the Hold, Write and Erase Modes. This constant current is obtained
by monitoring the current through the anode electrode of the
electrophoretic display by the sensing resistors 85.
It is understood that while the various relay configurations are
shown as electromechanical devices it is expressly understood that
solid state relays can be employed as well. In any event, such
relays for example as relays 32 and 24 could be supplied by
utilizing silicon controlled rectifiers. It is clear that the
function of such electromechanical relays can be replaced by solid
state devices.
* * * * *